1. Field of the Invention
This invention generally relates to improvements in the processing and storage of voice messages. Specifically, a voice message is split into a plurality of message blocks and stored on individual data storage devices. By recording the message on a plurality of data storage devices, if one or more of the data storage devices are unavailable, the other devices are used to reform the message in an intelligible form. During normal processing, the voice message is retrieved from all of the data storage devices and merged to reform the original voice message.
2. Description Of The Prior Art
The past several years have seen the exploitation of digital switch capabilities, particularly the ability to multiplex voice and data through the switch. A natural extension of this capability was the development of a mailbox capability for a user's telephone. This capability allowed much of the written correspondence associated with daily interaction to be replaced with voice communication stored and accessible from a person's phone.
A necessary feature of a voice mailbox system was a facility to store and retrieve a voice message. An example of a digitized voice message storage system is found in U.S. Pat. No. 4,549,047, to Brian et al., issued Oct. 22, 1985. The patent discloses a digital voice processing system that converts analog telephone signals into digital data which the system uses for message storage. The system has two levels of storage. A random access memory is used to temporarily store the messages, and a mass storage system is used to retain the messages for longer periods of time.
There are various limitations of the disclosed method. First, the messages are stored in a single location in the random access memory or mass storage system. This means that a single parity error, surface defect or other memory fault can distort or even destroy a message. Second, the messages are stored on a single memory subsystem. This means that a hardware problem can temporarily or permanently postpone recovery of a message.
Another approach for recording analog audio signals is to convert the analog samples into coded pulse groups as disclosed in U.S. Pat. No. 4,224,642, to Mawatari et al., issued Sept. 23, 1980. The patent discusses a technique for recording and reproducing analog audio signals and compensating for dropout errors induced by the recording medium. The successive pulse groups are recorded on different regions of a magnetic tape. To replay the messages, the pulse groups are reconverted into electrical signals from the recording medium and rearranged into the original order. While this technique allows some errors in the recording medium to be overcome, the sequential recall of information stored on a tape would make retrieval of randomly stored messages difficult. Also, the use of a single tape leaves the system subject to the loss of information resulting from a tape failure.
Another technique for pulse code modulation (PCM) signal recording is disclosed in U.S. Pat. No. 4,622,598, to Doi et al., issued Nov. 11, 1986. The disclosed method distributes the input PCM signals and records them so that one-channel PCM signals are recorded on a plurality of recording tracks. The words are encoded as a function of whether the input word numbers are even or odd, and the words thus separated are subjected to time delays or interleaving operations, after which the odd and even numbered words are recorded. This technique provides adequate protection against single track errors by distributing the signal over multiple recording tracks, but there is no capability provided for avoiding a unit failure.
An article entitled, "Minimum Redundancy Parts-Of-Speech Data Storage Technique", IBM Technical Disclosure Bulletin, Vol. 26, No. 11, April 1984, p. 6083 discloses a technique to reduce the storage necessary to store the basic parts of speech in a dictionary word list. This technique is similar to other compression algorithms that reduce the storage necessary for saving a digital message on a data storage device. None of the compression techniques provides a means for fractionalizing the original message and storing it on a plurality of data storage devices to allow the reformation of the original message from the divided original.
High availability systems that have an absolute requirement to conserve data storage space use techniques like that employed in the IBM System/88. The IBM System/88 has a pair of processors which automatically duplex each write operation to dual data storage devices. This technique, while effective for specialized data processing operations, is unacceptable for voice mailbox operations where data storage space is critical.
While the prior art discusses methods for distributing analog information on a single recording medium to decrease the effects of defects in the recording medium and the use of duplexed information to remedy failures in one of the copies, the prior art has no solution to the problem that our invention addresses.